Inhaled anesthetics are either volatile or gaseous anesthetics used to induce general anesthesia. Volatile anesthetics include halothane, enflurane, isoflurane, desflurane and sevoflurane. These anesthetics are liquid at room temperature. Gaseous anesthetics include nitrous oxide and xenon both of which are gaseous at room temperature.

00:00
And yes, we do paralyze patients! Modern
muscle relaxants are rapid in onset,predictable in recovery sequence, and have
minimal cardiovascular effects. But they produceno amnesia, and no analgesia. And one
of the great errors that occurs in anesthesia,is to think that a muscle relaxant is an anesthetic.
They're used primarily in surgical procedureswhere muscle relaxant is necessary for adequate
surgical access. This is most commonly abdominalsurgery, thoracic surgery and surgery
on heavily muscled areas, such as the thigh.
00:35
They're also used so the anesthetist or other physician
can secure the airway with minimal trauma tothe patient. It paralyzes the muscles
of the airway, allowing the vocalcords to remain open, and makes it easier
to place an endotracheal tube.
00:53
It's often used when patients who require prolonged
ventilation in the operating room, or inthe intensive care unit. They prevent
movement. They prevent breathing.
01:05
They prevent escape, the patients can't get away.
But they do NOT produce analgesia.
01:11
And probably even more importantly,
they do NOT produce amnesia.
01:17
Do not produce sleep
or unconsciousness directly.
01:23
So they are not anesthetics, they are adjuncts
to anesthesia, and their usedin the absence of drugs that cause amnesia
or drugs that produce analgesia, is verybad practice. One of the nice things about muscle relaxants
is that, amongst all the drugs used by anesthesiologists,they're about the only drugs we actually know
exactly how they work. They either causedepolarization of muscle fibers in what
is referred to as an irreversible action,this is the depolarizing muscle relaxant
succinylcholine, or they competitivelyblock depolarization of muscle fibers
by competing with normal neuro-transmitters,non-depolarizing muscle relaxants,
and the newest of all of these is Rocuronium. So,depolarizing muscle relaxants actually
pass across the neuromuscular junctionto the muscle end-plate and cause
depolarization of the muscle. In other words,they act as if they were a normal neuro-transmitter
and cause normal contraction of the muscle. However,this contraction is brief,
and we refer to it as fibrillations,when we can see the twitching of the muscles,
and it's irreversible. The drug just sitsthere and doesn't allow the muscle to repolarize,
which is the normal sequence, in normally functioningmuscles. Now, that's not to say that it stays
forever. It tends to get diluted over timein normal body fluids. And there is a substance
in most people, called Pseudocholinesterase,which will break down Succinylcholine and get rid
of it in a really quite rapid fashion.
03:05
However, we'll talk briefly about this
in another lecture wherepeople do not have Pseudocholinesterase.
The more commonly used drugs noware non-depolarizing muscle relaxants. So they don't cause
the fasciculations that you get with Succinylcholine.
03:23
And what happens with them is,
they pass across the neuromuscular junction,they attach themselves to the neuromuscular
end-plate, and theysit there for a period of time. But they are
in competition with Acetylcholine, whichis the normal neuro-transmitter. Anything
that tends to increase the concentrationof Acetylcholine, will reduce the effect
of the muscle relaxant. Anything that tendsto reduce the effectiveness, or the presence
of Acetylcholine, will increase the effectivenessof the muscle relaxant. And this
is kind of a diagram of how thesedrugs work. They change the polarization
of the neuromuscular sarcolemma,the surface of the muscle, so that there's
a movement of sodium and potassiumin opposite directions, and there's
a change in polarity, which results in an actionpotential. Acetylcholine does this by opening upchannels that allow depolarization
of the muscle fiber.
04:35
Non-depolarizing muscle relaxants block
the effect of Acetylcholine by competingfor those same receptors. And Succinylcholine
causes depolarization, but it doesn'tallow repolarization. And without
the cycles continuing, depolarizationand repolarization, no further
contractions can occur.

About the Lecture

The lecture Muscle Relaxants – Gases and Induction Drugs by Brian Warriner, MD is from the course Anesthesiology: Introduction.

Included Quiz Questions

Succinylcholine:

Produces relaxation by irreversible depolarizing block

Is a useful amnestic when used alone.

Is reversed by acetylcholinesterase.

Rarely, if ever, causes allergic reactions.

Author of lecture Muscle Relaxants – Gases and Induction Drugs

Brian Warriner, MD

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